Wire matrix ballistic impact print head

ABSTRACT

A wire matrix ballistic impact print head for delivering printing impacts to a record medium under control of information format control circuitry and including a plurality of impact print wires or styli, a guide for translating the plurality of styli from a circular arrangement at the impact delivering end of the styli, a plurality of electromagnetic actuators for selectively driving the styli during a print cycle of operation of the print head, and a unitary connector for maintaining the armature of each electromagnetic actuator in proper positional alignment with a print stylus, for simultaneously adjusting all armatures to approximately the same de-energized position, for preventing bounce of the armature after an energized actuator is de-energized and for establishing a reference plane to which all styli are referenced.

[ 51 Dec. 30, 1975 [54] WIRE MATRIX BALLISTIC IMPACT PRINT HEAD [75] Inventor: Donald G. Hebert, San Ramon,

Calif.

[73] Assignee: D & D Associates, Mountain View,

Calif.

[22] Filed: Sept. 18, 1974 [21] Appl. No.: 507,060

Primary Examiner-Edgar S. Burr Assistant Exam'inerR. T. Rader Attorney, Agent, or FirmSchatzel & Hamrick [57] ABSTRACT A wire matrix ballistic impact print head for delivering printing impacts to a record medium under control of information format control circuitry and including a plurality of impact print wires or styli, a guide for translating the plurality of styli from a circular arrangement at the impact delivering end of the styli, a plurality of electromagnetic actuators for selectively driving the styli during a print cycle of operation of the print head, and a unitary connector for maintaining the armature of each electromagnetic actuator in proper positional alignment with a print stylus, for simultaneously adjusting all armatures to approximately the same de-energized position, for preventing bounce of the armature after an energized actuator is deenergized and for establishing a reference plane to which all styli are referenced.

9 Claims, 9 Drawing Figures CONTROL -42 CIRCUITRY US. Patent Dec. 30, 1975 Sheet 3 of3 3,929,214

WIRE MATRIX BALLISTIC IMPACT PRINT HEAD BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to printing apparatus, and more particularly, to a high-speed matrix-type ballistic impact print head.

2. Description of the Prior Art High speed printers have been developed to accomodate the high output speed of information which can be delivered by high speed information handling systems. The operational speed of such printers, however, is still a limiting factor as tothe total efficiency of an information handling system in that the printers are still relatively slow when compared to the speed of the electronics generating the information to be printed. Therefore, any improvement which increases the operational speed of the printer has a marked effect on the overall efficiency of the operating system.

Printers employing wire matrix ballistic impact print heads provide multiple hard copies of information at a relatively high speed. These printers are characterized in that for each print cycle, the printer does not print an entire character per impact but instead use an array of wire styli to print selected combinations of dots serially onto the recording medium so that as the recording medium is moved relative to the print head, successive print cycles generate alpha-numeric characters or other informational indicia.

One major factor dictating the speed at which the wire matrix ballistic impact print head is capable of operating is the inertia associated with the impacting styli and the electromechanical stylus armatures. Print heads of this type typically use a separate electromagnetic actuator for each stylus within the print head. A major problem encountered by the prior art in designing such heads is the physical space required to accomodate these actuators within the print head while maintaining the inertia of the print head as low as possible. Further, electromagnetic actuator and stylus combination must be individually adjusted. Thus, the adjustment for making all styli strike the record medium at approximately the same instant of time during a print cycle is more complex, difficult and time consuming.

BRIEF SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a high speed wire matrix ballistic impact print head wherein the actuators are arranged in a circle so as to reduce the inertia of the print head.

It is another object of the present invention to provide a high speed wire matrix ballistic impact print head which employs a unitary connector for holding the armatures of each actuator in proper positional alignment with its associated stylus.

Another object of the present invention is to provide a high speed wire matrix ballistic impact print head which employs a unitary connector for simultaneously adjusting all the actuators within the print head such that all actuated styli strike the record medium at substantially the same instant of time.

It is still another object of the invention to provide a high speed wire matrix ballistic impact print head having a shock absorbing medium for preventing bounce of the actuator armature and/or stylus during the return portion of a print cycle thereby preventing spurious imprinting on the record medium.

Briefly, the high speed wire matrix ballistic print head includes a plurality of wire styli inserted for movement within a guide. The guide translates the circular formation of the impact receiving ends of the styli to a straight line formation of the impact delivering ends of the styli. An individual actuator is provided for engaging the impact receiving end of each stylus. A unitary connector is also provided which includes means for holding the armature in contact with a magnetic structure to form an actuator means for holding each armature in proper alignment with its associated stylus, means for simultaneously adjusting the air gap between the armature and the electromagnet of the actuator, means forming a reference surface for referencing all styli, and damping means for eliminating bounce of the armatures and styli after the actuators are deactivated during a print cycle.

An advantage of the present invention is that it minimizes the variance in length of the styli, thereby allowing the simultaneous adjustment of the position of all styli within the guide.

Another advantage of the print head is that the print head includes a unitary multifunction connector instead of the plurality of individual connectors as in the prior art, thereby reducing the mass of the print head.

Still another advantage of the present invention is the use of a unitary connector for providing simultaneous adjustment of all actuators such that all of the styli strike the record medium at substantially the same time.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention illustrated in the several figures of the drawing.

IN THE DRAWING FIG. 1 is a perspective view of a print head in accordance with thepresent invention;

FIG. 2 is a cross'sectional view taken along the line 2-2 of FIG. 1 illustrating the major components of the print head;

FIG. 3 is a front elevational. view of the guide shown in FIG. 1;

FIG. 4 is a plan view of the second translation element of the guide shown in FIG. 3;

FIG. 5 is a plan view of the third translation element of the guide shown in FIG. 3;

FIG. 6 is a bottom view of the fourth translation element of theg'uide shown in FIG. 3;

FIG. 7 is a schematic diagram showing the electrical connectors of the actuator coils for the print head shown in FIG. 1;

FIG. 8 is a plan view of the print head shown in FIG. 1 with the unitary connector and the armatures of the actuators removed; and

FIG. 9 is a bottom view of the unitary connector shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A print head I0 in accordance with the present invention is shown in FIG. I connected to control circuitry 12 by means of the wires 14 and a plug 16. A ribbon 18 is disposed in between the bottom of print head 10 and paper 20.

FIG. 2 is a side elevational cross-section view illus trating the major components of the print head 10.

3 Only one actuator and one stylus is shown in order to simplify the drawing. It should be understood that nine actuator/stylus combinations, identical in structure to that shown in FIG. 2, are included within the structure of print head 10.

A guide 22 is provided for receiving a stylus 24 and constraining it to move along a curved path. The stylus 24 has a plastic cap 26' attached to its impact receiving end to enlarge the area of the impact receiving surface. Stylus 24 has a spring 28 disposed at its upper end which exerts an upward force upon cap 26 to resiliently bias stylus 24 upwardly relative to guide 22. Guide 22 includes four translational guide elements 30, 32, 34 and 36, which accomplish the translation of the nine styli 24 from a circular formation in the first guide element to a straight line formation in the fourth guide element 36. The translation is accomplished by passing each stylus 24 through a separate hole 38 in the first element 30, through a separate hole 40 in the second element 32, through a separate hole 42 in the third element 34 and into a defined position within a bearing 44 of the fourth element 36.

FIG. 3 illustrates a front elevational view of guide 22 showing a side wall 46 and a side wall 48 terminating in the fourth translation element 36. Side wall 46 and a sidewall 48 are provided with two sets of facing grooves 50 and 54 and 52 and 56 for receiving the edges of guide elements 32 and 34 respectively. At one edge of sidewall 46 the grooves 50 and 52 extend deeper into the sidewall to form keyways for receiving the locating key tabs 64 and 66 of guide elements 32 and 34.

A pair of mounting flanges 58 and 60 extend laterally from the upper ends of side walls 46 and 48. Guide 22 is configured circular in shape above flanges 58 and 60, and terminates in a circularly aperatured surface which forms first guide element 30. A post 62 extends from the first translation element 30.

FIG. 4 is a plan view of the second guide element 32 showing the styli guide holes 40 arranged in an eliptical pattern. The key 64 extends from the side of element 32 to orientate the placement of element 32 within guide 22 as mentioned above.

FIG. 5 is a plan view of the third guide element 34 showing the location of the styli guide holes 42. As illustrated, the arrangement of the guide holes 42 is of a generally elongated oval configuration more or less intermediate the eliptical configuration shown in FIG. 4 and the straight line configuration shown in FIG. 6. The key 66 extends from the side of element 34 for orientating the element within guide 22.

FIG. 6 is a bottom view of the fourth guide element 36 of guide 22 showing the location of bearing 44 within guide 22. Bearing 44 aligns the lower ends, the impacting ends, of the plurality of styli 24 in the desired linear arrangement. The bearing 44 is of a material which resists wear, has a low coefficient of friction and has a low coefficient of thermal expansion.

Returning to FIG. 2, a base plate 70 is used as the base for the construction of the print head 10. Plate 70 is provided with a central aperture 72 through which the circular portion of guide 22 extends. A plurality of holes 83 are provided in the base plate 70 for mounting the nine actuators thereto. Guide 22 is connected to base plate 70 by means of the mounting flanges 58 and 60 (see FIG. 2) which are affixed to the lower surface of plate 70.

A coil 74, a center pole 76, an L-shaped outer pole 78 and an armature 80 form the electromagnetic actuators used in the print head. A hole 82 is provided in the horizontal leg of the L-shaped outer pole'78 for receiving the lower extremity of center pole 76. Hole 82 has a diameter which is the same as the outer dimension of center pole 76 so as to provide a forced fit therebetween. The center pole 76 of each actuator has a threaded lower end 84 which extends through the hole 83 in base plate 70. The center pole 76 and outer pole 78 combination is held in place by a nut 86 threaded onto end 84.

A wiring/connector board 88 (see also FIG. 1) has a opening 90 provided therein for receiving an outer pole 78. Board 88 also has an aperture 92 through which the circular portion of guide 22 extends. Nine additional holes 93 are provided in board 88 through which the nine center poles 76 of the nine actuators pass. Coil 74 is mounted around the center pole 76 on each actuator and wired to the wiring/connector board 88.

FIG. 7 is a schematic diagram illustrating the electrical connection of the actuator coils 74 to the board 88. The nine coils 74 are wired with one end of each coil 74 commonly connected and the other end of each coil 74 wired to a separate connection point on edge connector 91 which is formed integral with board 88 as shown in FIG. 8.

In FIG. 8 a plan view of the print head 10 is shown with the armatures 80 and the unitary connector 94 removed. In essence, FIG. 8 illustrates the construction of the print head 10 up to the point heretofore described. The nine stylus heads 26 are shown positioned above the first guide element 30 of guide 22. Board 88 is shown mounted between the coils 74 and the magnetic structures formed by the center poles 76 and the outer poles 78 of the nine actuators. Mounting holes 95 are provided in base plate 70 for mounting the completed print head 10 to a printing system. The post 62 of guide 22 has a threaded hole 96 provided therein.

Returning to FIG. 2, the unitary connector 94 is mounted by means of a screw 97 and washer 98 to the post 62 of guide 22. Screw 97 passes through opening 130 in connector 94 and threads into the opening 96 of post 62. Connector 94 has a circular central portion 100 with an annular groove 102 provided in its bottom surface. An O-ring 104 is inserted in groove 102 to act as a shock absorber and to provide a reference surface for the stylus striking ends of the armatures 80.

Nine arms 106 extend from central portion 100. Each arm 106 has associated with it a first armature receiving structure 108 and a second armature receiving structure 110. One end of each armature 80 is received and held in place by structure 108 and the other end of each armature is received and guided by structure 110. Where connector 94 is installed in the position shown, arms 106 apply forces to the cantilevered distal ends of the armatures causing their stylus impacting ends to rotate about the fulcrum formed by the top edge of pole 78 and upwardly into engagement with O-ring 104. The heads 26 of the styli 24 are maintained in contact with the ends of armatures 80 by means of the forces applied by the springs 28.

FIG. 9 is a bottom view of the unitary connector 94 showing one armature 80 located in position relative to one .of the arms 106. On its outermost end, the armature 80 has notches 112 and 114 which mesh with first and second walls 116 and 118 of the first receiving structure 108 of arm 106. The central portion 100 has nine armature receiving structures formed around its periphery. Structure 110 is formed by first and second walls 120 and 122. At its innermost extending end 126, armature 80 is narrowed so that it passes between the two walls 120 and 122 of the receiving structure 110. The O-ring 104 provides a reference surface against which all of the armatures 80 are referenced.

Unitary connector 94 serves six separate and distinct functions. First, it holds each armature 80 in contact with the corresponding outer pole 78 (along line 124) so as to complete the magnetic circuit of the actuator as used within the print head 10. Second, it acts as a resilient, force applying member applying a moment to each armature 80 causing it to tend to rotate about the outer pole 78 and away from the contact with the corresponding stylus 26.- Armature 80 is thereby rockably mounted upon pole 78 with its narrow end portion 126 in contact with the reference surface formed by O-ring 104. Third, the unitary connector acts as a means for aligning the end 126 of each armature 80 with the cap 26 of its corresponding stylus 24. This alignment feature prevents undesired lateral movement of armature 80 and insures that armature 80 is in proper aligning contact with stylus cap 26. Fourth, connector 94acts as an adjusting means for simultaneously adjusting the air gap (see FIG. 2) between each of the armatures 80 (at point 128) and the corresponding center poles 76 of the respective actuators. As a result of this adjustment, the position of all the styli 24 are uniformly adjusted within guide 22. Fifth, connector 94 forms a reference surface against which the armatures 80 and cap 26 of styli 24 are referenced such that all actuated styli 24 impact the record medium at substantially the same instant of time during a print cycle. Sixth, the unitary connector 94 includes a shock absorbing O-ring 104 which absorbs the energy of the armatures 80 and styli 24 as they return to their rest positions when the actuators are deactivated. The absorbtion of the kinetic energy within a particular armature 80 and stylus 24 at the end of a print cycle prevents the armature 80 or the stylus 24 from bouncing and thereby causing spurious imprints following the print cycle.

Returning to FIG. 2, the screw 97 is passed through hole 130 and tightened to pull the center portion 100 down toward post 62. As screw 97 is tightened, the air gap between center pole 76 and armature 80 will decrease. At the same time the moment exerted on armature 80 by arm 106 is increased. By the judicious adjustment of screw 97 an optimum setting can be obtained for transmitting the most desirable amount of energy into stylus 24 by armature 80 while maintaining a desirable speed of return .of armature 80 to its rest positions,

In the alternative, the two-piece structure of the outer pole 78 and centerpole 76 could be replaced by a single, cast structure of suitable material. Further, if increased efficiency of the magnetic circuit is desired, additional outer poles could be designed into the actuator to improve the magnetic circuit associated with the actuator- Here again, the multi-pole structure could be constructed of a plurality of separate elements or could be made of a single cast structure of proper material. The base plate 70 could also be included into any casting so as to lower the cost of manufacturing.

Operation of the Preferred Embodiment Referring to FIG. 1, print head is capable of generating nine impressions during each print cycle. Alpha-numeric characters or other information is generated by a sequence of print cycles. For example, the

letter E" is formed by selectively activating various combinations of the nine styli 24 during five separate print cycles. Normally, the top seven styli 24 are used to generate letters having no below-the-line projections. Letters requiring below-the-line formation are printed using in addition the lower two styli. An example is that illustrated by the lower case letter g.

The control circuitry 12 selects which combination of the nine styli 24 will be actuated during each print cycle. In between each print cycle, the print head 10, in one printer embodiment, is moved one print increment with respect to the paper 20 and the ribbon 18. However, the relative movement can be made either by moving only print head 10, or by moving only paper 20 and ribbon 18, or by moving the print head 10 and the paper 20 (and the ribbon 18). k I

The smaller the print increment, the greater the resolution of information imprinted on paper 20. The printing speed of print head 10 allows high resolution information to be generated within. a reasonable time. The information generated may take the form of both upper and lower case printed letters, script, pictures, figures, mathematical notations, etc.

Referring to FIG. 2, when the coil 74 is energized, a magnetic flux is created which will cause armature to be drawn into contact with center pole 76. The movement of armature 80 will transmit energy into stylus 24 causing the stylus 24 to move downwardly through guide 22. The force imparted into stylus 24 causes it to move against spring 28 and its inertia causes it to continue to move downwardly out of contact with armature 80 after the armature bottoms out against pole 76 as shown by the dashed lines. The impact delivering end of stylus 24 extends beyond bearing 44 and strikes the record medium causing a dotto be imprinted. The energy stored in the moving stylus 24 is partially absorbed by the impacted medium and partially returned to stylus 24 aiding spring 28 in returning stylus 26 to its rest position. v

At approximately the same time that stylus 24 is impacting the record medium, the coil 74 is de-energized. The moment exerted on armature 80 by arm 106 causes it to rotate away from the center pole 76 and to return into contact with O-ring 104. The energy in the returning armature 80 and the stylus 24 is absorbed by the dampening material of the 'O-ring 104 thereby preventing bounce of either armature 80 or stylus 24, thus preventing spurious imprints to be made during a print c cle.

It has been found that optimum'energy is transmitted into the stylus 24 when the actuators air gap is set such that the impacting end of the armature 80 moves a distance of 0.015 inch. It has also been found that the total distance moved by the stylus 24 should be approximately 0.030 of an inch so that the stylus is in free flight for approximately 0.015 inch. Accordingly, the clearance between the bottom of the print head and the print medium should be set at approximately 0.030 inch.

While the invention has been particularly shown and described with reference to'a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A wire matrix ballistic impact print head comprismg:

' a base;

stylus guide means affixedto said base;

N electromagnetic structures mounted to said base and disposed around said guide means, each of said electromagnetic structures having an outer pole, a center pole coupled to said outer pole, and a coil disposed around one of said poles;

N armatures disposed radially about said guide means, each of said armatures being associated with one of said electromagnetic structures to form an electromechanical actuator for transferring electromechanical energy to a stylus, and each of said armatures having a stylus engaging end and an outer end that extends in cantilevered fashion outside of said outer pole;

N styli carried by said guide means, each of said styli being of an elongated rod-like configuration having a head end for engagement by the stylus engaging end of one of said armatures and a printing end for impacting a recording medium when the stylus is propelled through said guide means by one of said actuators;

a unitary connector having a central portion connected to said guide means and N resilient arms extending radially outward therefrom, each of said arms engaging the outer end of one of said armatures for applying a moment of force thereto tending to cause the stylus engaging end to rotate about said outer pole toward said central portion.

2. A wire matrix ballistic impact print head as recited in claim 1 wherein said central portion includes a shock absorbing means against which the stylus engaging end of each of said armatures is held by said moments of force when the actuator associated therewith is deenergized. i

3. A wire matrix ballistic impact print head as recited in claim 2 wherein the central portion of said connector is affixed to said guide means by an adjusting means which when tightened causes said connector to be pulled towards said base to simultaneously adjust the air gaps between the armature and the center pole of each of said electromagnetic actuators.

4. A wire matrix ballistic impact print head as recited in claim 1 wherein each of said arms further includes means for holding the stylus engaging ends of each of said armatures in operative alignment with a corresponding one of said styli.

5. A wire matrix ballistic impact print head as recited in claim 4 wherein said central portion includes a shock absorbing means mounted therein and against which the stylus engaging end of each of said armatures is held by said moments of force when the actuator associated therewith is deenergized.

6. A wire matrix ballistic impact print head as recited in claim 4 wherein said central portion is affixed to said guide means by an adjusting means whichwhen tightened causes said connector to be pulled towards said base to simultaneously adjust by like degree the air gaps and between the armature and the center pole of each of said electromagnetic actuators.

7. A wire matrix ballisitc impact print head as recited in claim 5 wherein said unitary connector further includes an adjusting means for simultaneously adjusting the air gap between the armature and the center pole of each of said electromagnetic actuators.

8. A wire matrix ballistic impact print head as recited in claim 1 wherein said N electromagnetic structures are arranged in a circular array on said base and wherein said printing ends of said styli are aligned in a row.

9. A wire matrix ballistic impact print head comprising:

a base plate having a central aperture;

a guide connected to said base plate and extending through said central aperture, the top end of said guide having N guide apertures arranged in a circular array, and the bottom end of said guide having N guide apertures arranged in a straight line array;

N springs;

N styli, each having an enlarged head at one end and passing through one of said springs, through one of said guide apertures in said top end of said guide and through one of said guide apertures in said bottom end of said guide, said springs serving to resiliently bias said styli into a rest position;

N electromagnetic structures connected to said base plate, each of said structures having an outer pole, a center pole coupled to said outer pole, and a coil mounted around one of said poles;

wiring means connecting one end of each of said coils in common;

electrical connecting means forming individual connections to the other ends of each of said coils and through which each of said coils may be energized;

N elongated armatures each having a stylus engaging end and an outer end, and each being associated with one of said electromagnetic structures and pivotable about one of said outer poles, the respective combinations of armature and electromagnetic structure forming N electromagnetic actuators for selectively propelling various ones of said styli through said guide apertures; and unitary connector coupled to said base plate and including a central portion having a shock absorbing means and N arms radiating from said central portion, each of said arms (1) engaging one of said outer ends to hold the associated armature in contact with one of said outer poles to form an electromagnetic actuator, (2) holding the associated armature in alignment with one of said heads of one of said styli, and (3) providing a moment of force to the associated armature tending to cause the armature to rotate about the associated outer pole and into engagement with said shock absorbing means, said connector further including an adjustment means for enabling'the air gaps between the armatures and the center poles of each of said electromagnetic actuators to be adjusted simultaneously. 

1. A wire matrix ballistic impact print head comprising: a base; stylus guide means affixed to said base; N electromagnetic structures mounted to said base and disposed around said guide means, each of said electromagnetic structures having an outer pole, a center pole coupled to said outer pole, and a coil disposed around one of said poles; N armatures disposed radially about said guide means, each of said armatures being associated with one of said electromagnetic structures to form an electromechanical actuator for transferring electromechanical energy to a stylus, and each of said armatures having a stylus engaging end and an outer end that extends in cantilevered fashion outside of said outer pole; N styli carried by said guide means, each of said styli being of an elongated rod-like configuration having a head end for engagement by the stylus engaging end of one of said armatures and a printing end for impacting a recording medium when the stylus is propelled through said guide means by one of said actuators; a unitary connector having a central portion connected to said guide means and N resilient arms extending radially outward therefrom, each of said arms engaging the outer end of one of said armatures for applying a moment of force thereto tending to cause the stylus engaging end to rotate about said outer pole toward said central portion.
 2. A wire matrix ballistic impact print head as recited in claim 1 wherein said central portion includes a shock absorbing means against which the stylus engaging end of each of said armatures is held by said moments of force when the actuator associated therewith is deenergized.
 3. A wire matrix ballistic impact print head as recited in claim 2 wherein the central portion of said connector is affixed to said guide means by an adjusting means which when tightened causes said connector to be pulled towards said base to simultaneously adjust the air gaps between the armature and the center pole of each of said electromagnetic actuators.
 4. A wire matrix ballistic impact print head as recited in claim 1 wherein each of said arms further includes means for holdinG the stylus engaging ends of each of said armatures in operative alignment with a corresponding one of said styli.
 5. A wire matrix ballistic impact print head as recited in claim 4 wherein said central portion includes a shock absorbing means mounted therein and against which the stylus engaging end of each of said armatures is held by said moments of force when the actuator associated therewith is deenergized.
 6. A wire matrix ballistic impact print head as recited in claim 4 wherein said central portion is affixed to said guide means by an adjusting means which when tightened causes said connector to be pulled towards said base to simultaneously adjust by like degree the air gaps and between the armature and the center pole of each of said electromagnetic actuators.
 7. A wire matrix ballisitc impact print head as recited in claim 5 wherein said unitary connector further includes an adjusting means for simultaneously adjusting the air gap between the armature and the center pole of each of said electromagnetic actuators.
 8. A wire matrix ballistic impact print head as recited in claim 1 wherein said N electromagnetic structures are arranged in a circular array on said base and wherein said printing ends of said styli are aligned in a row.
 9. A wire matrix ballistic impact print head comprising: a base plate having a central aperture; a guide connected to said base plate and extending through said central aperture, the top end of said guide having N guide apertures arranged in a circular array, and the bottom end of said guide having N guide apertures arranged in a straight line array; N springs; N styli, each having an enlarged head at one end and passing through one of said springs, through one of said guide apertures in said top end of said guide and through one of said guide apertures in said bottom end of said guide, said springs serving to resiliently bias said styli into a rest position; N electromagnetic structures connected to said base plate, each of said structures having an outer pole, a center pole coupled to said outer pole, and a coil mounted around one of said poles; wiring means connecting one end of each of said coils in common; electrical connecting means forming individual connections to the other ends of each of said coils and through which each of said coils may be energized; N elongated armatures each having a stylus engaging end and an outer end, and each being associated with one of said electromagnetic structures and pivotable about one of said outer poles, the respective combinations of armature and electromagnetic structure forming N electromagnetic actuators for selectively propelling various ones of said styli through said guide apertures; and a unitary connector coupled to said base plate and including a central portion having a shock absorbing means and N arms radiating from said central portion, each of said arms (1) engaging one of said outer ends to hold the associated armature in contact with one of said outer poles to form an electromagnetic actuator, (2) holding the associated armature in alignment with one of said heads of one of said styli, and (3) providing a moment of force to the associated armature tending to cause the armature to rotate about the associated outer pole and into engagement with said shock absorbing means, said connector further including an adjustment means for enabling the air gaps between the armatures and the center poles of each of said electromagnetic actuators to be adjusted simultaneously. 